Brainteaser and math puzzle thread

[TheDean1]

Feels like there should be one of these where people can just drop random brainteasers and try to answer them and whatnot. I'll go first:

In celebration of Mets's 75k post, he and HiFi decide to host a party and invite 10 other couples (22 total ppl at the shin dig) . Throughout the course of the party, Mets decided to keep track of the handshaking going on and surveyed the entire party (i.e. everyone including HiFi but not himself). Note that although Mets isn't part of the data sample directly, somebody else shaking his hand does count toward their respective tally. He found 2 noteworthy facts

1) Everybody that he surveyed shook a different number of hands
2) Nobody shook hands with their spouse/significant other/etc

How many hands did HiFi shake?

[ibavly]

You have 3 people. One person always tells the truth, one always lies, one sometimes tells the truth sometimes lies. You can ask three questions. You ask each one one question, one person 2, w/e you want to do.

How do you figure out who is who?

btw I think it is a given that if you already know the riddle don't post the answer, if you solved it then you should probably still use spoilers.

[ibavly]

another one I like:

You have a table with a switch on 4 corners and a light in the middle. If all the switches are on or all the switches are off when you end the round the light turns on. You don't know how they are set up before. After each round, the table spins so you don't know which switch is which. What is the smallest number of rounds it will take to guarantee the light turning on.

[switch0723]

well my brain just melted

answers should be included after the questions to give peace of mind imo

[ibavly]

are all the other couples POGers?

[ibavly]

The answer to deans puzzle. I strongly recommend trying to figure it out on your own since it's so much more rewarding. I was asked the puzzle in post#2 when I was a kid and the person wouldn't tell me the answer, and I just kept thinking about it at random times for about a year til I figured it out. Just seeing the answer is not satisfying at all.

Spoiler:

(shakes)(couple)
0/1 - no one
1/2 - 20/1
2/ -
3/ -
4/ -
5/ -
6/
7/
8/
9/
10/11 (hifi)
11/
12/
13/
14/
15/
16/ -
17/ -
18/ -
19/2 - everyone but 0/1 and SO
20/1 - everyone but 0/1
mets/11

[pwnsall]

What's in my pocket?

[ibavly]

a church!

[pwnsall]

Originally Posted by ibavly

another one I like:

You have a table with a switch on 4 corners and a light in the middle. If all the switches are on or all the switches are off when you end the round the light turns on. You don't know how they are set up before. After each round, the table spins so you don't know which switch is which. What is the smallest number of rounds it will take to guarantee the light turning on.

never

[ESKiMO-SiCKNE5S]

Originally Posted by ibavly

You have 3 people. One person always tells the truth, one always lies, one sometimes tells the truth sometimes lies. You can ask three questions. You ask each one one question, one person 2, w/e you want to do.

How do you figure out who is who?

btw I think it is a given that if you already know the riddle don't post the answer, if you solved it then you should probably still use spoilers.

Spoiler:

ask one of them the same question 3 times.

if he changes his answer then he is the one who sometimes lies. if he doesnt, then he is one of the others.

[evilhamit]

Originally Posted by ESKiMO-SiCKNE5S

Spoiler:

ask one of them the same question 3 times.

if he changes his answer then he is the one who sometimes lies. if he doesnt, then he is one of the others.

Spoiler:

I don't think this works, if he sometimes lies he may lie all 3 times (or tell the truth 3 times). Also you would only know who 1 person is, but not the other two

[theHuntContinues]

Originally Posted by ibavly

The answer to deans puzzle. I strongly recommend trying to figure it out on your own since it's so much more rewarding. I was asked the puzzle in post#2 when I was a kid and the person wouldn't tell me the answer, and I just kept thinking about it at random times for about a year til I figured it out. Just seeing the answer is not satisfying at all.

Spoiler:

(shakes)(couple)
0/1 - no one
1/2 - 20/1
2/ -
3/ -
4/ -
5/ -
6/
7/
8/
9/
10/11 (hifi)
11/
12/
13/
14/
15/
16/ -
17/ -
18/ -
19/2 - everyone but 0/1 and SO
20/1 - everyone but 0/1
mets/11

Your questions and your solutions are extremely badly written and it's impossible for anyone to figure out what you are trying to say.

The explanation that makes sense to you in your head is very often insufficient for other people.

[theHuntContinues]

Originally Posted by ibavly

You have 3 people. One person always tells the truth, one always lies, one sometimes tells the truth sometimes lies. You can ask three questions. You ask each one one question, one person 2, w/e you want to do.

How do you figure out who is who?

btw I think it is a given that if you already know the riddle don't post the answer, if you solved it then you should probably still use spoilers.

what would be the answer to a question that is not a true/false proposition?

i.e. pick a number from 1-10

is each person aware of the truth-nature of others?

if an answer can be chosen between two options by one of the persons, would they answer randomly or would they answer with all options?

[theHuntContinues]

Originally Posted by ibavly

another one I like:

You have a table with a switch on 4 corners and a light in the middle. If all the switches are on or all the switches are off when you end the round the light turns on. You don't know how they are set up before. After each round, the table spins so you don't know which switch is which. What is the smallest number of rounds it will take to guarantee the light turning on.

Can you even manipulate the switch? What can I do? Am I just merely and observer?

[theHuntContinues]

Here is a question I was asked by ibavly, i couldn't find the answer so maybe you guys can do better;

something happened then other something might happen if another something happens but that another something only happens if some random thing happens which you don't know which is which because the state of something happening is randomised after each round. What is the 386958573930748th digit of pi?